(1) Field of the Invention
The present invention relates to a writing instrument having a function of an automatic mechanical pencil in which lead is automatically fed when a front end of the writing instrument is lifted from a writing surface during a writing operation, and a function of a shaking-type mechanical pencil in which lead is fed by shaking the writing instrument.
(2) Description of Related Art
A writing instrument having a function of an automatic mechanical pencil and a function of a shaking-type mechanical pencil is disclosed, for example, in Japan Published Utility Model No. 63-191080. The writing instrument of this type has a slider frictionally holding the lead at the front end of a barrel cylinder, and the slider is disposed to undergo movement in an axial direction and is urged in the forward direction by a spring. A lead chuck, e.g., a ball chuck, is disposed rearwardly of the slider to undergo movement in the axial direction and holds the lead in such a manner as to allow forward movement of the lead but prevent backward movement thereof. A weight is movably disposed rearwardly of the lead chuck. During writing, the slider retracts as the lead abrades and is consumed, and when the front end of the writing instrument is separated or lifted from the paper, the slider advances while holding the lead, whereby the lead is automatically fed. Further, when the barrel cylinder is shaken, the weight moves forward and backward and impacts the lead chuck, whereby the lead chuck advances to feed the lead.
In known writing instruments of this type, the weight can freely move and collide with a member disposed at the end of its movement stroke, whereby the member may be damaged. When this member is, for example, a knocking button attached to the barrel cylinder, the knocking button may become detached. Further, such known writing instruments have a complicated structure, cannot be easily altered to cancel the function of a shaking-type mechanical pencil so as to limit the mechanical pencil to the function of an automatic mechanical pencil, and cannot be used as a knocking-type mechanical pencil.